The present invention relates to a tribometer for testing the slip resistance of various surfaces. More particularly, the present invention relates to a portable variable incidence tribometer, for measuring the slip resistance of wet or oily surfaces as well as dry, which approximates the forces present during the walking process.
A tribometer is a device used for measuring surface friction. Tribometric devices utilize various methods for determining the frictional force present when one surface is pulled or pushed across another under a certain predetermined pressure. These devices fall within three generally recognized categories; (1) dragsled, (2) articulated strut and (3) pendulum type testers. Numerous tribometric devices in each category exist, which are disclosed in a number of United States Patents, which test the frictional forces between different dry surfaces.
One problem which exists and which is not overcome by these devices is obtaining consistent surface friction results on surfaces which are wet or have lubricating contaminants thereon. Because of the increased risk of slippage which exists when a surface is wet a reliable method of testing these surfaces is needed.
In situations where it is desired to determine the slip resistance of a wet surface unreliable results can occur due to the effects of absorbtion and squeegeeing. These effects result in devices where the test specimen is allowed to rest on the test surface prior to motion testing so that the contaminants are either absorbed by the test specimen or squeezed out from beneath it.
Attempts have been made to provide devices which can reliably test the slip resistance on different surfaces including wet surfaces. These attempts are described as follows.
U.S. Pat. No. 4,798,080 discloses a portable apparatus which tests the slip resistance of surfaces by substantially instantaneously applying a load to a frictional pad. The load in this device is applied using a gravity dropped weight or a spring.
U.S. Pat. No. 4,895,015 discloses a portable horizontal slipmeter in which a stationary pull mechanism applies a force to a drag sled. The drag sled with the test specimen attached is held away from the test surface until the device is actuated.
Leon Bennett, M.A.E. and Eugene F. Murphy, Ph.D., Slipping Cane and Crutch Tips, bulletin of prosthetics research for 1977, page 71, discloses an instrumented walking cane used for testing the slip resistance of cane tips on various walking surfaces. Instrumentation is provided on this device to show the angle of incidence and magnitude of the force vector at the point where the cane tip slips.
It has also been suggested to provide a variable incidence mast fitted with an articulated cane that is thrust downward at a predetermined angle in order to test the slip resistance of a cane tip. This device utilizes an electric solenoid to provide the downward thrust.
The prior art devices have many limitations. In particular, the devices which employ weights, springs or solenoids for the thrust force are not representative of the forces which are present during the walking process.
Additionally, the devices which require the application of thrust force by the operator are subject to operator dependent variables. These operator dependent variables tend to bias the results of the slip tests so that consistent results are difficult to achieve.
A further limitation exists in devices which utilize gravitational force. This limitation results in the inability to obtain valid results on inclined surfaces without recalibration. Since it is often necessary to determine the coefficient of friction of an inclined surface, this inability substantially limits the application of these devices.